Ultrasonic method for the production of inorganic/organic hybrid nanocomposite

ABSTRACT

The present invention provides a method for producing organic/inorganic hybrid nanocomposites by use of ultrasonic agitation. The particles are reacted with an organic coupling agent to modify the surface of said particles to inhibit agglomeration.

BACKGROUND OF INVENTION AND PRIOR ART

1. Field of the Invention

The present invention relates to a method for fabricating nanocomposite,particularly, organic-inorganic hybrid nanocomposite and nanocompositesproduced thereby.

In the present method, the combination of ultrasonic irradiation andsurface modification/functionalization of nanoparticles is, for thefirst time, employed for producing nanocomposite.

2. Prior Art Related to the Invention

Ultrasonic irradiation has been very well recognized as one of energysources used by chemists for a long time. Ultrasonic irradiation differsfrom traditional energy sources, such as heat, light, or ionizingradiation, in duration, pressure, and many other aspects. The chemicaleffects of ultrasound do not come from a direct interaction withmolecular species. Instead, it principally derives from acousticcavitation: the formation, growth, and implosive collapse of numerousbubbles in a liquid. Acoustic cavitation serves as a means ofconcentrating the diffuse energy of sound. Bubble collapse induced bythe cavitation produces short-lived, but intense local heating (hotspots) and high-pressure spots (Suslick et al., J. Am. Chem. Soc. 108,5641 (1986)). In heterogeneous liquid-solid systems, cavitation nearextended liquid-solid interface is very different from the cavitation inpure liquids. Two mechanisms are proposed for the effects of cavitationnear the surface of solids: microjet impact (Lauterborn et al., 16, 223,(1984)) and shock wave damage (Doktycz et al., Science 247, 1067(1990)). According to Lauterborn supra, the asymmetry of the environmentnear the interface induces a deformation of the cavity during itscollapse. This deformation is self-reinforcing, and it sends afast-moving stream of liquid through the cavity at the surface withvelocities greater than 100 m/s . The second mechanism ofcavitation-induced surface damage invokes shock waves created by cavitycollapse in the liquid (Doktycz supra). The shock waves created byhomogeneous cavitation can create high-velocity interparticlecollisions. The impingement of microjets and/or shock waves on thesurface creates the localized erosion responsible for ultrasoniccleaning and many of the sonochemical effects on heterogeneous reaction(Suslick, Science 3, 1439 (1990)).

In summary, ultrasonic energy can be principally employed fordispersing, crushing/pulverizing, freshening (cleaning) particles, andin some cases, activating surfaces of particles, as well as initiatingsome chemical reactions.

Practically, ultrasonic irradiation has been widely used for vesselcleaning in both scientific laboratories and industries.

Ultrasonic irradiation has also been widely used as an energy source fordispersing pigments and/or particles, including nanoparticles, intoimmiscible media in both scientific laboratories and industries. Thisapplication has resulted in a number of patents, including DE 2656330(1976), DE 2842232 (1978), EP 308600 (1987), EP 308933 (1988), EP 434980(1989), WO 92/00342 (1990), DE 4328088 (1993), and EP 434980 (U.S. Pat.No. 5,122,047). In these applications, surfactants (dispersants) areusually used for purposes of reducing particle surface energy, and laterparticle surface protection, therefore stabilizing the produceddispersion/suspension. Without the surface protection, the dispersedparticles, particularly the nanoparticles, would unavoidablyre-agglomerate in some degree due to their extremely high surfaceenergy. However, very often, these surfactants were unwanted, sometimeseven considered as contaminated materials for the end applications.

The use of high intensity ultrasound to enhance the reactivity of metalsas stoichiometric reagents in many heterogeneous organic andorganometallic reactions has attracted more and more attention (Suslick,Adv. Organomet. Chem. 25, 73 (1986); Lindley et al., Chem. Soc. Rev. 16,239,275 (1987); Suslick, “Ultrasound: Its Chemical, Physical, andBiological Effects” (VCH, New York, 1988); Luche, Ultrasonics 25, 40(1987); Kitazume et al., J. Am. Chem. Soc. 107, 5186 (1985)).

Nanocomposites have been shown to offer tremendous improvements inmechanical and physical properties at very low loading levels for anumber of polymeric resins. These attributes can provide affordableperformance and/or improved tailor-ability for many industrialapplications. Going from the micro- to the nanoscale introduces someunique aspects: at the nanoscale, specific surface area is very high,resulting in an increased effect of interface at low filler volumes, andfiller size is approaching the scale of the polymer chain.Nanocomposites have often shown unexpected property improvements in manyaspects.

Developing a reliable and economic method for production ofnanocomposite materials is becoming a major challenge. Many approacheshave been tried, and they are listed as follows:

-   -   1. The vapor deposition techniques, Akamatsu et al.,        Nanostructured Materials, 8, 1121 (1997) including chemical        vapor deposition (CVP) or physical vapor deposition (PVD).    -   2. Precursor techniques, Watkins et al., Polym Mater. Sci. Eng.,        73, 158 (1995) mainly belong to sol-gel types of chemistry. The        precursors of nanoparticles (e.g. alkoxides of Si or other        metals), often are first introduced in a pre-polymeric/        polymeric matrix, then nanoparticles are generated in this        matrix through appropriate chemical reactions.    -   3. Micelle or inverse micelle techniques, Mayer et al., Colloid        Polym Sci, 276, 769 (1998); Chemical & Engineering News, 25-27,        Jun. 7, 1999) where the precursors of nanoparticles are        introduced into nanoscale domains, such as micelles or inverse        micelles, resulting from the amphiphatic block or graft polymer,        and particles form in situ through appropriate chemical        reactions, such as reduction. The size of the particles is        limited by the size of nanoscale domains.    -   4. Intercalation/Exfoliation of nano-platelets (such as        nanoclay) into polymeric matrix, Qiao et al., Acta Polymer        (China), 3, 135 (1995).    -   5. Super-molecule self-assembly technique, Weller, Adv Mater,        5(2), 193 (1993) by a complicated self-assembly process, the        nanoscale super-molecular structure of fiber, layer, or tube can        be produced.    -   6. Encapsulating polymerization, Bourgeat-Lami et al, Polymer,        36(23), 4385 (1995), where nanoparticles are first dispersed        into a pre-polymeric/polymeric matrix, then, under proper        conditions, the polymerization of monomer occurs on the surface        of nanoparticles, forming polymer layer encapsulating particles.    -   7. Nanoparticle surface initiated polymerization, Sugimoto,        “Fine Particles”, 626-646 Marcel Dekker, Inc. New York, Basel        (2000). This approach involves “growing” polymers directly from        surfaces of nanoparticles. The general technique of this        approach is to attach a convenient organic functionality to the        particle. Nanocomposites can be produced through standard        organic transformation reactions, such as polymerization.

Methods 6. and 7. appear to be two of the most promising approachesbecause of their diversified raw material sources, simple and adaptableproduction process, and high tailoring capability for a variety ofindustrial applications.

The method in the present invention is believed to belong to method 7.

The incorporation of nanoparticles into an immiscible (in many cases,organic) matrix represents one of the most difficult problems in thefabrication of nanocomposites. The success in the manufacturing of suchmaterials can be achieved only if the aggregation of particles isavoided, and the nanoparticles are distributed in the matrixhomogeneously.

Ultrasonic energy has been used to disperse one liquid metalliccomponent in a second immiscible liquid metal, thereby producing ametallic emulsion. Upon lowering the temperature of this emulsion belowthe melting point of the lowest-melting constituent, ametal/metal-matrix composite is formed (Keppens et al., “Nanophase andNanocoposite Materials II Materials Research Society SymposiumProceedings”, 457, 243-248 (1997). No real chemistry takes place in theprocess.

Ultrafine amorphous Si/C/N powders are obtained using ultrasonicinjection of a liquid precursor (hexamethyldisilazane: HMDS) into thebeam of a high power industrial cw-CO₂ laser (Herlin et al., Journal ofthe European Ceramic Society, 13(4), 285-291 (1994).

Chinese patent 1280993 and a published article by the same authors (Wanget al., C. Journal of Applied Polymer Science, 80(9), 1478-1488 (2001)reported that ultrasound induced encapsulating emulsion polymerizationwas first used to prepare the novel polymer/inorganic nanoparticlescomposites. Here, ultrasound and both cationic and anionic surfactantswere used for emulsion preparation. The activation behavior ofnanoparticles in the aqueous solution under ultrasonic irradiation wasalso reported. More interestingly, they have reported the successfulultrasound induced emulsion polymerization of n-butyl acrylate (BA) andmethyl methacrylate (MMA) without any chemical initiator. However, asuspicion resulted from their experimental section that the acrylatesolution/emulsion was deoxygenated. Therefore, emulsion polymerizationof the monomers might be simply caused by the removal ofoxygen-inhibition and heat generated by ultrasonic irradiation.

Chinese patent CN 1216297 describes a process for activatingnanometer-level powder, such process comprising:

-   -   stirring nanometer level Si—H—O composite powder, subjecting to        vaccum treatment to remove the absorbed water on the surface of        the powder, storing under inert gas and irradiating with        gamma-ray    -   stirring the powder, subjecting to scattering treatment by        ultrasonic vibration. The active nanometer level composite        obtained can be coupled with a polymer initiated by a        silicone-type coupling.

Nano-sized materials have at least one linear dimension having a meansize between 0.1 and 250 nm. Preferably, the mean size is less than 100nm. Nano-sized materials exist with the nano-size in three dimensions(nano-particles), two dimensions (nano-tubes having a nano sized crosssection, but indeterminate length) or one dimension (nano-layers havinga nano-sized thickness, but indeterminate area). Preferred aspects ofthe present invention relate to nano-sized materials comprisingnanoparticles.

Nano-sized materials (II) are generally of mineral nature. They cancomprise aluminum, oxide, silica, etc.

Published prior art WO 00/69392 describes transparent or translucentphotopolymerizable composites for dental and medical restoration. Thecomposites contain zirconium oxide nanoparticles whose surface isfunctionalized with a coupling agent which is preferably zirconate. Thephotopolymerizable composite is formed by mixing a solution ofnanoparticles with a solution of a suitable matrix monomers andphotoinitiator. There is no dispersion step of the nanoparticles usingultrasound irradiation.

SUMMARY OF THE INVENTION

An objective of this invention is to combine ultrasonic irradiation andnanoparticle surface modification to provide a more efficient andeffective method for producing nanocomposite, particularly,organic-inorganic hybrid nanocomposite materials. This combinationprovides multiple process-functions including dispersing particles intoorganic media, crushing/pulverizing particles to desired nano-scale, andfreshening (cleaning) the surface of nanoparticles for the followingsurface modification reactions. More importantly, through microjetsand/or shock waves, ultrasonic irradiation diffuses bulky surfacemodifying agents onto nanoparticle surfaces, and also possibly,activates/accelerates surface modification reactions due to effects of“local hot spot” mentioned above. Under ultrasonic irradiation, particlecrushing/pulverizing with simultaneous surface modification effectivelyprevents re-agglomeration of nanoparticles. Lack of any one of above twoprocess-elements will cause either re-agglomeration or inhomogeneousnanocomposites.

Another objective of the invention is to allow one to use cheap, powderform nanoparticles as raw materials for nanocomposite production. Manynanoparticle product suppliers provide powder form “nanoparticle”products, in which their actual particle size are actually several ortens of microns due to re-agglomeration. The suppliers claim that theprimary particle size of their products is smaller than 100 nm.Colloidal types of nanoparticle products usually have a much morecontrollable particle size and particle size distribution. However, theprices of these products are much higher.

The third objective of the invention is to provide a method to makehybrid nanocomposite materials that can be, preferably, radiation (e.g.,UV/electron beam) curable, and also thermally curable.

Another objective of the invention is to provide a method to make hybridnanocomposites, in which inorganic nanophases are covalently bonded withorganic networks.

Another objective of the invention is to provide a method to make hybridnanocomposites with extremely high homogeneity with a single and narrowparticle-size distribution peak in the nano-scale.

Another objective of the invention is to provide a method to make hybridnanocomposite materials with better rheological behavior, therefore,better processability than those hybrid nanocomposite materials preparedwithout ultrasonic treatment and/or without surface modification.

Another objective of the invention is to provide a method to make hybridnanocomposite materials that form cured coatings/films with bettersurface hardness than those formed solely from base-resins ortraditional filler systems.

Another objective of the invention is to provide a method to make hybridnanocomposite materials that form cured coatings/films with bettersurface scratch resistance than those formed solely from base-resins ortraditional filler systems.

Another objective of the invention is to provide a method to make hybridnanocomposite materials that form cured coatings/films with higherabrasion resistance than those formed solely from base-resins ortraditional filler systems.

Another objective of the invention is to provide a method to make hybridnanocomposite materials that form cured coatings/films with bettersolvent/chemical resistance than those formed solely from base-resins ortraditional filler systems.

Another objective of the invention is to provide a method to make hybridnanocomposite materials that form cured coatings/films with higherimpact resistance than those formed solely from base-resins ortraditional filler systems.

Another objective of the invention is to provide a method to make hybridnanocomposite materials that form cured coatings/films with higherstorage modulus than those formed solely from base-resins or traditionalfiller systems.

Another objective of the invention is to provide a method to make hybridnanocomposite materials that form cured coatings/films with higher lossmodulus than those formed solely from base-resins or traditional fillersystems.

Another objective of the invention is to provide a method to make hybridnanocomposite materials that form cured coatings/films with morecontrollable Tg (glass transition temperature) than those formed solelyfrom base-resins or traditional filler systems.

Another objective of the invention is to provide hybrid nanocompositematerials that form cured coatings/films with better weather-abilitythan those formed solely from base-resins or traditional filler systems.

The present invention seeks to achieve these objectives by fabricatingnanocomposite, particularly, organic-inorganic hybrid nanocompositematerials.

More specifically, the present invention provides a method for producingorganic/inorganic hybrid nanocomposites which comprises:

-   -   a. subjecting a dispersion with inorganic particles to        ultrasonic agitation to produce a dispersion of nanosized        inorganic particles, and    -   b. reacting the nanosized inorganic particles from step a. with        an organic coupling agent to modify the surface of said        particles to inhibit agglomeration of said particles.

DETAILED DESCRIPTION OF THE INVENTION

The present method produces the nanoparticle composites by ultrasonicagitation alone or in combination with mechanical agitation.

The mechanical agitation and ultrasonic agitation may be performedsequentially or simultaneously.

Suitable inorganic particles include alumina, other metal oxides,silica, carbon, metals, etc.

Suitable organic coupling agents include organozirconates,organotitanates and organosilanes. Neopentyl (diallyl)oxy triacrylzirconate) is an example.

Suitable coupling agents include coupling agents providing, in additionto better compatibility between inorganic and organic matrix,polymerizable/crosslink-able reactivity, preferably, UV curablefunctionality. Those coupling agents may comprise at least one(meth)acrylate functionality.

Additionally, there may be employed an adhesion promotor and suitableadhesion promotors include 3-methacryloxytrimethoxysilane,3-glycidoxypropyltrimethoxysilane and other organosilanes.

Further, the instant hybrid nanocomposites are suitable for use inradiation curable compositions comprising the nanocomposite and theradiation curable resin.

Suitable radiation curable resins include at least one of the threefollowing reactive components:

-   -   1) one or more radiation polymerizable reactive oligomers or        prepolymers, the molecular weight of which is generally lower        than 10,000 and which have, at the chains ends or laterally        along the chain, acrylic, methacrylic, vinyl or allyl groups.    -   2) one or more polyethylenically unsaturated reactive monomers        which contain at least two ethylenically unsaturated groups.        These reactive monomers are preferably diacrylates or        polyacrylates of polyols of low molecular weight. The essential        role of these reactive monomers is to enable adjustment of the        viscosity depending on the intended industrial application.    -   3) one or more monoethylenically unsaturated reactive monomers        which contain only one ethylenically unsaturated group per        molecule. Examples of such monomers are the monoacrylates or        monomethacrylates of monohydric or polyhydric aliphatic        alcohols. Other examples of such monomers are styrene,        vinyltoluene, vinylacetate, N-vinyl-2-pyrrolidone,        N-vinylpyridine, N-vinylcarbazole, and the like. These monomers        are added to the compositions as reactive diluents in order to        lower the viscosity. These monomers can also have a considerable        influence on the physical and chemical properties of the final        coatings obtained. The reactive monomers used in the radiation        curable compositions should have the following properties:        -   low toxicity        -   low volatility and odor        -   low viscosity        -   high reactivity.

However, current commercially available monomer systems fail tocompletely fulfill these prerequisites at the same time. Compromise mustbe made since in general, with these systems,

-   -   the lower the viscosity of the monomer, the lower reactivity of        the formulation at a given monomer content and    -   the lower the viscosity of the monomer, the higher the        volatility and the lower the human olfactory threshold.

Besides the above-mentioned reactive components, the radiation curablecompositions may contain various auxiliary constituents to adapt them totheir specific technical applications.

Optionally, a photoinitiator especially in combination with a tertiaryamine is added to the composition so that, under the influence ofultraviolet irradiation, the photoinitiator produces free radicals whichinitiate the crosslinking (curing) of the composition. Thephotoinitiator is, for example, benzophenone, benzil dimethylketal,thioxanthones, and the like.

The proportions (ranges) of the foregoing materials are as follows:

Nanoparticles-1 to 30% by wt. of the total nanocomposite formulation.

Coupling agents-0.1 to 5.0% by wt. of the nanoparticles.

Radiation curable resins-60 to 95% by wt. of the total nanocompositeformulation.

Photoinitiators-1 to 6% by wt. of the total radiation curable resincomposition.

Adhesion promotors 0.5 to 5% by wt. of the total nanocompositeformulation.

There will now be described examples of embodiments according to thepresent invention. These embodiments are merely exemplary and are notintended to limit the present invention in any manner.

EXAMPLES

Equipment:

Ultrasonic Liquid Processor used in the invention was obtained fromSonic & Materials, Inc. The model is Vibra-Cell 130; it generatesultrasonic irradiation with the frequency of 20 kHz and the output poweris 130 watts.

Materials:

1. Aluminum Oxide C, Al₂O₃ powder with average primary particle size(TEM) of 13 nm was obtained from Degussa-Huls. It was used as received.

2. MA-ST-S, silica nanoparticle dispersion in methanol with averageprimary particle size of 8-10 nm was obtained from Nissan Chemicals.

3. NZ-39, neopentyl (diallyl) oxy triacryl zirconate, was obtained fromKenRich Petrochemicals Inc.

4. Z-6030, 3-methacryloxypropyltrimethoxysilane, was obtained from DowCorning Corp. It was used as adhesion promoter.

5. Tabular Alumina, micron-sized alumina filler, was obtained from AlcoaChemicals

6. Tripropylene Glycol Diacrylate(TRPGDA) Monomer was UCB Chemicals'tri-functional monomer. It was used as a part of the base resin.

7. Eb 8402 is UCB Chemicals' difunctional aliphatic urethane acrylateoligomer. It was used as a part of the base resin.

8. Eb 1290 is UCB Chemicals' six-functional aliphatic urethane acrylateoligomer. It was used as a part of the base resin.

9. Irgacure 184 was obtained from Ciba Inc. It was used as PI.

10. D.I. water was made in UCB Chemicals' Analytical Lab by using theNANOpure system from Barnstead/Thermarlyne Inc. The quality of D.I.water always meets the electronic resistance number of 18M□-cm.

Test Methods

1. DMA tests were performed on DMA 2980 (Dynamic Mechanical Analyzer)from TA Instruments. The tests provided data of storage modulus, lossmodulus and Tg of the cured films.

2. Pencil Hardness ASTM D 3363-This test method covers a procedure forrapid determination of the film hardness of a coating on a substrate interms of drawing leads of known hardness.

3. Abrasion Resistance of Organic Coatings by the Taber Abraser, ASTM D4060-84—The coating is applied at uniform thickness to a Leneta chart,and, after curing, the surface is abraded by rotating CS-17, 500 gweighted wheels. Coatings are subjected to 50 or more cycle intervals ofabrading. If after the 50-cycle interval, there is any sign ofbreakthrough to the substrate, the testing is terminated. Loss in weightat each 50-cycle interval is also calculated.

4. Scratch Resistance The test panel is held firmly in one position anda 4″×4″ eight layered square of steel wool (˜1 cm thick), covering a twopound ball peen hammer is rubbed back and forth across the coating,counting each back and forth motion as one double rub. The handle of thehammer is held in as close to a horizontal position as possible and nodownward pressure is exerted on the hammer. At the first sign ofscratching, haze, or breakthrough to the substrate, the counting andtest are terminated.

5. Impact Resistance Procedure is the same as ASTM D 2794

6. MEK Resistance (Chemical Resistance by Solvent Rub)—SMT 160-K (UCBChemicals' test method) The test panel is held firmly in one positionand a 4″×4″ eight layered square of cheese cloth, covering a two poundball peen hammer is soaked with MEK, and the hammer is rubbed back andforth across the coating, countings each back and forth motion as oneMEK double rub. The handle of the hammer is held in as close to ahorizontal position as possible and no downward pressure is exerted onthe hammer. At the first sign of breakthrough to the substrate, thecounting and test are terminated.

7. Adhesion ASTM D 3359-95A (Measuring Adhesion by Tape Test)—An areafree of blemishes and minor surface imperfections is selected. Two cutsare made in the film, using a multi-tip cutter for coated surfaces. Thecoated substrate is placed on a firm base, and parallel cuts are made.All cuts are about ¾ in. (20 mm) long. The film is cut through to thesubstrate in one steady motion using just sufficient pressure on thecutting tool to have the cutting edge reach the substrate. After makingthe required cuts, the film is lightly brushed with a tissue or softbrush to remove any detached flakes or ribbons of coatings. The cutareas are then covered with one-inch wide semitransparentpressure-sensitive tape. The tape is then removed and discarded. Theareas are then brushed and inspected for percent of area removed: 5B=0%,4B=Less than 5%, 3B=5-15%, 2B=15-35%, 1B=35-65%, 0B=Greater than 65%.

8. Cylindrical Mandrel Bend Tests A conical mandrel test consists ofmanually bending a coated metal panel over a cone. As described in ASTMTest Method for Elongation of Attached Organic Coatings with ConicalMandrel Apparatus (D 522), a conical mandrel tester consists of a metalcone, a rotation panel bending arm, and panel clamps. These items areall mounted on a metal base. The cone is smooth steel 8 in. in lengthwith a diameter of ⅛ in. at one end and a diameter of 1.5 in. at theother end. When a coating is applied on a {fraction (1/32)}-in.-thickcold-rolled steel panel, as specified in ASTM S 522, a bend over themandrel produces an elongation of 3% at the large end of the cone and of30% at the small end of the cone. The coated panel is bent 135° aroundthe cone in approximately 1 second to obtain a crack resistance ratingunder simulated abuse conditions. In this study, the length of crackingwas then measured and reported.

9. Particle Size and Particle Size Distribution Analysis Nanoparticlesamples were analyzed using a Coulter LS230 Particle Size Analyzer. Thisinstrument uses laser light scattering to detect particles in the rangeof 0.04 to 2,000 micrometers. Samples were fully dispersed in methanolafter shaking for three minutes. Particle size data was collected andaveraged over 90 seconds for each run. The size calibration of themethod was checked using reference standards at 15 and 55 micrometers

Control Samples:

For comparison purposes, three control-samples were made in thisinvention.

Their compositions are listed in the Table 1. The performance comparisonof the invented nanocomposites with these control samples are listed theTables 3, 4, and 5. The photoinitiator levels in every formulation ofboth control-samples and nanocomposites are always 4% of UV-resinweight. The procedures for preparation of films/coatings of thecontrol-samples, the cure conditions for these control samples, and theproperty test methods are all the same as that for the inventednanocomposite samples described below. TABLE 1 Mixture of UV- Resins asNeat UV-Resin Traditional Filler Control as Control System Compositionsample I Parts sample II Parts Control sample III Parts Particles No NoMicro size Al₂O₃ 10 Surface No No No Modifying Agents Adhesion No No Nopromoter Organic Eb 8402/ 100 Eb 1290 100 Eb 8402/TRPGDA 90 Base TRPGDA(50/50) Resins (50/50) Photoinitiator Irgacure 4 Irgacure 184 4 Irgacure184 3.60 184 Total 104 104 103.60 Corresponding Reaction

EXAMPLE 1

The first example, RX 05505, shows preparation of nanocomposite via thecombination of ultrasonic irradiation and surfacemodification/functionalization of nanoparticles. KenRich PetrochemicalsInc provides neoalky zirconate (titanate and etc.), chelated titanate(or zirconate and etc.), monoalkoxy titanate (or zirconate and etc.) assome examples of coupling agents. Typically, NZ 39, named neopentyl(diallyl) oxy triacryl zirconate was employed in this example. By usingthis coupling agent, nanoparticle surface modification provides, inaddition to better compatibility between inorganic and organic matrix,polymerizable/crosslink-able reactivity, preferably, UV curablefunctionality. The molecular structure of this coupling agent isrepresented as follows.

The composition of this nanocomposite is shown in Column 1 in Table 2TABLE 2 EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 Nano- Nano- Nano- Compositioncomposite(I) Parts composite(II) Parts composite(III) Parts ParticlesAl₂O₃ 10.0 Al₂O₃ 4.32 SiO₂ 10.0 SiO₂ 1.08 Surface NZ-39 0.05 NZ-39 0.05NZ-39 0.05 Modifying Agents Adhesion Z-6030 0.48 0.0 Z-603 1.03 promoterCatalyst 0.0 Acrylic acid 1.00 D.I. Water 0.0 H₂O 0.24 Organic Base Eb8402/ 91.03 Eb 8402/ 94.53 Eb 1290 88.9 Resins TRPGDA TRPGDA (50/50)(50/50) Photoinitiator Irgacure 3.64 Irgacure 184 3.78 Irgacure 184 4.0184 Total 99.99 103.78 105.22 Corresponding RX 05505 RX 01399 RX 05596Reaction

The Al₂O₃ nanoparticles (Alumina C) in powder form was firstmechanically dispersed into methanol by stirring with magnetic bar. Theratio of Al₂O₃ to methanol was about 1/20-1/50. A milk white dispersionwas obtained after two hours of agitation.

The stability of this dispersion (Sample 1) was poor. Precipitation wasseen 10-15 minutes after the agitation was stopped. With only mechanicalagitation, the alumina particles could only reach 15-20 microns onaverage.

Therefore, the combination of mechanical agitation and ultrasonicirradiation was employed as per the present invention. One hour ofultrasonic irradiation and mechanical agitation effectively crushed andpulverized agglomerated alumina C particles to nano-scale (121 nm inaverage). The new dispersion (Sample 2) shows much better stability thanSample 1. However, the dispersed nanoparticles still couldre-agglomerate, and the precipitation was seen after setting at roomtemperature for 1-2 days (see Sample 2). It is worthy to note that theprecipitates at the bottom of Sample 2 are much less than that of Sample1.

Furthermore, the surface of the nanoparticles was protected bysurface-modification in the present invention.

A coupling agent, NZ-39, was dissolved in methanol to make 1-5%solution. At room temperature, the solution was then drop-wise addedinto the dispersion under conditions of a combination of ultrasonicirradiation and mechanical agitation. The amount of surface modifyingagent used in the reaction depends on the reactivity of the couplingagent, the molecular size of the coupling agent, the type and size ofthe particles, the surface structure of the particles, as well as theavailable number of reactive groups on the surface of the nanoparticles.In this example, the amount of NZ-39, based on the particles (AluminumOxide in this case) weight, can be varied from 0.1-5.0%. The surfacemodification reaction normally takes place at room temperature. However,in order to ensure completion of the reaction, the mixture should berefluxed at 60□C. for two hours.

After surface modification, the Aluminum Oxide dispersion was verystable. Organic molecule attachments on the surface of nanoparticlesnormally cause an increase in nanoparticle size. However, the sizedistribution peak of the modified nanoparticles is narrower, and theaverage of the particle size is even smaller: 118 nm. This fact stronglyindicates that under ultrasonic irradiation, simultaneous surfacemodification is significantly helpful in the crushing/pulverizingparticle process.

A more interesting phenomenon was seen: the surface modified Alumina Cparticles became much more hydrophobic, and therefore, less compatiblewith hydrophilic methanol. The dispersion showed two organic layers, butno precipitation at the bottom of the container (Sample 3). As ahydrophobic solvent, such as toluene, was added into the dispersion withsimple shaking, the two layers disappeared, and a stable dispersion wasobtained (Sample 4). There was no precipitation after setting at roomtemperature for at least two months.

Then, the dispersion (Sample 3) was easily and homogeneously mixed withorganic resins, preferably, UV-curable resins in the present invention.In this example, the mixture of Eb8402/TRPGDA with 50/50 ratio was usedas the base resin. The composite material normally contains 1.0%-10%,but possibly high as 40% by weight of modified nanoparticles based onthe total formulation weight. The solvent, methanol, contained in thematerial was evaporated at 40□C. with gradually increased vacuum valuesof the system from 240 millibar to 50 millibar. Through this “solventexchange” operation, at least 97%, and more often, 100% of the methanolcould be evaporated. Therefore, the nanocomposite material becomes 100%reactive. More clearly, the inventive nanocomposites contain bothorganic resins and modified nanoparticles, which are reactive, andpreferably, UV-curable.

4 parts of photoinitiator (Irgacure 184 in the present invention), basedon weight of UV-curable materials, was homogeneously mixed into theproduced nanocomposite materials to form the final formulation.

The produced liquid nanocomposite material is very stable after 10months no precipitation or significant viscosity changes have been seen.

EXAMPLE 2

Following the procedures described in Example 1, with one change,produced another nanocomposite, RX 01399. The composition of thisnanocomposite is listed in Column 2 of Table 2. Instead of solely usingAl₂O₃ nanoparticles as in Example 1, the combination of Al₂O₃ and SiO₂nanoparticles were employed.

Again, the produced nanocomposite material was stable for at least 10months without seeing precipitation or significant viscosity changes.

Approximately 0.5-6 mil films/coatings) were drawn down on ParkerBonderite 40 steel panels. The thickness of coatings/films depend on the# of the drawing bar and the viscosity of the materials. The panels thenwere cured in air using one or two 300 watt/inch mercury vaporelectrodeless lamps, at the maximum belt speed that gave tack-free(cured) films/coatings.

The properties of these films/coatings were then tested according to themethods described above.

The property data listed in Table 3 clearly indicate the advantages ofthe invented nanocomposite.

In comparison to UV-resins, the traditional filler system has shown someimprovements in MEK resistance, abrasion resistance and Tg. However,under production conditions, the phase separation between inorganic andorganic phases in these systems has been always a big problem for longtime. Also because of this problem, the material property can only betailored in a very narrow range.

The nanocomposite shows surface performance improvements in everycategory except adhesion and impact resistance. The poor adhesion isbelieved due to lack of reactive hydroxyl groups (for interaction withsubstrate surface) in this material.

DMA tests also indicate that the loss and storage modulus and Tg of thenanocomposite are all improved. Moreover, the variation inmulti-parallel DMA test results is much smaller for the inventednanocomposites than for those composite samples without ultrasonictreatments or for those composite samples without surface modification.This implies higher homogeneity in the invented nanocomposite. It isbelieved that this improvement is closely related to smallernanoparticle size, the narrower distribution of nanoparticle size, andhomogeneously diffusing nanoparticles in the nanocomposites. TABLE 3Mixture of Traditional UV-Resins as Filler Nanocomposite (II) PROPERTYControl Sample System With Al₂O₃ and SiO₂ APPEARANCE Newtonian PhaseViscous liquid, liquid Separation pseudo-plastic UV-DOSAGE 2.8-3.52.8-3.5 2.8-3.5 (J/cm²) SURFACE 5-6H 5-6H 9H PENCIL HARDNESS MEK 70-11090-110 170-190 RESISTANCE ABRASION 50 cycles 100 cycles 100 cyclesfailed RESISTANCE failed IMPACT 50-70 lb.-inch 42-44 60-70 RESISTANCEADHESION ON 3B 0B 1B STEEL PANEL Tg (Loss Mod.) 34 □C 48 □C 51 □CStorage Modulus 1336 (MPa) 1716 (MPa) 2105 (MPa) (@ 25□C) Loss Modulus 147 (MPa)  181 (MPa)  173 (MPa) (@ Tg)

EXAMPLE 3

Following the preparation procedures described in Example 1 and 2another nanocomposite was prepared. The composition is listed in Column3 of Table 2.

Eb 1290 was used as the base resin in this example. Eb 1290 is UCBChemicals' six-functional aliphatic urethane acrylate oligomer, whichprovides greater than 9H surface hardness and very good surface scratchresistance. However, it is extremely brittle. The purpose of making thisnanocomposite is to increase the flexibility without loss of otheradvantages of Eb 1290, such as hardness and scratch resistance.

A small amount of silane, Z-6030, was added for adhesion promotion. Atthe same time, a very small amount of acrylic acid was added as thecatalyst for hydrolysis and condensation reactions, and an equivalentamount of water was added for hydrolysis reaction of the silane.

The performance data of the nanocomposite in Table 4 indicateimprovements in flexibility reflected as impact resistance and conicalbend. Note that, adhesion is also increased.

More dramatically, abrasion resistance of the invented nanocompositeincreases greatly from 100 cycles to greater than 20,000 cycles withoutfailure. At the same time, the advantages of Eb 1290 remain. TABLE 4Neat UV-Resin as Control Nanocomposite (III) PROPERTY sample II WithSiO₂ and Silane APPEARANCE Newtonian, viscous Viscous liquid, liquid at60□C pseudo-plastic at 25□C UV-DOSAGE    0.6    0.6 (J/cm²) SURFACEPENCIL >9H >9H HARDNESS MEK RESISTANCE >200 >200 ABRASION 100 cycles20,000 cycles RESISTANCE failed without failure SCRATCH >200 >200RESISTANCE (steel Wool double rubs) IMPACT    8    16 RESISTANCElb.-inch ADHESION ON 3B 4B-5B STEEL PANEL Conical Bend 0 inch failed 4inch failed

Table 5 presents more details regarding improvements of abrasionresistance. In addition, the weight lost per abrading cycle for theinvented nanocomposite significantly decreases. TABLE 5 CS-17 TestResults (failed-broken through, Sample weight lost: □g/cycle) Coatingthickness: □ 0.5 mil. Control 100 cycles, Sample Failed, Eb 1290 66.0 RX05596 100 cycles, 1,000 cycles, 10,000 cycles, 20,000 cycles, Passed,0.0 Passed, 3.6 Passed, 2.2 Passed, 2.0

1. A method for producing an organic/inorganic hybrid nanocompositewhich comprises: a. subjecting a dispersion of inorganic particles toultrasonic agitation to produce a dispersion of nanosized inorganicparticles having at least one linear dimension having a mean sizebetween 0.1 and 250 nm; and b. reacting the nanosized inorganicparticles from step a. with an organic coupling agent to modify thesurface of said particles to inhibit agglomeration of said particles. 2.The method according to claim 1 wherein the particles of step a. aresubjected to both ultrasonic and mechanical agitation.
 3. The methodaccording to claim 2 wherein ultrasonic and mechanical agitation areperformed simultaneously.
 4. The method according to claim 2 whereinultrasonic and mechanical agitation are performed sequentially.
 5. Themethod according to claim 1 wherein the inorganic particles are at leastone of metals, metal oxides, carbon and silica.
 6. The method accordingto claim 1 wherein the cotipling agent is at least one or organosilanes,organotitanates and organozirconates.
 7. The method according to claim 1wherein the coupling agent provides polymerizable/crosslinkablereactivity.
 8. The method according to claim 1 wherein the couplingagent provides radiation-curable functionality.
 9. The method accordingto claim 8, wherein the coupling agent comprises at least one(meth)acrylate functionality.
 10. The method according to claim 1wherein an adhesion promoter is additionally employed in step b.
 11. Themethod according to claim 10 wherein the adhesion promoter is anorganosilane.
 12. The hybrid nanocomposite produced according toclaim
 1. 13. A radiation curable composition comprising the hybridnanocomposite according to claim 12 and a radiation-curable resin. 14.The radiation curable composition according to claim 13 additionallycomprising a photoinitiator.